Synthesis and electrochemical properties of Li2S–B2S3–Li4SiO4

New Li⁺ ion-conductive glasses Li₂S–B₂S₃–Li₄SiO₄ were synthesized by rapid quenching, and they were transformed into glass ceramics by heat treatment. The heat treatment increased the ionic conductivities of the Li₄SiO₄-doped glasses, and the highest ionic conductivity observed in the system was 1.0 × 10^− 3 S cm^− 1 at room temperature. The glass ceramics were highly stable against electrochemical oxidation with a wide electrochemical window of 10 V.     

Electronic to ionic conductivity of glasses in the Li2S–Sb2S3–P2S5 system

There is great interest in sulfide glasses because of their high lithium ion conductivity. New sulfide glasses in the Li₂S–Sb₂S₃–P₂S₅ system have been synthesized by classical quenching technique. The glass domain relays on the medium-lithium content (up to 50% molar).Electrical conductivities of the samples have been determined by Impedance Spectroscopy. The isothermal conductivity curves exhibit two regions on dependence of lithium content implying that the conductivity mechanisms in these two regions are different. The compositions of low lithium content (below 20% mol.) have presented low electronic conductivities close to 10^− 8 S/cm at room temperature. The compositions of medium lithium content (30–50% mol.) could be mixed ionic–electronic conductors with predominant ionic conductivities with a maximum close to 10^− 6 S/cm for sample with 50% Li₂S at room temperature. Arrhenius exponential behavior is verified between 25 °C and T_g for all glasses. The activation energies, determined from temperature dependence, are 0.55–0.64 eV. A comparative study with glasses belonging to the other chalcogenide systems has been undertaken on base of the weak electrolyte model and the values of decoupling index, R_τ, are reported. The impedance of the 0.5Li₂S–0.3Sb₂S₃–0.2P₂S₅ ionic conductor can be described by an equivalent circuit R(RQ)(RQ).     

High lithium ion conducting glass-ceramics in the system Li2S–P2S5

Highly ion-conductive Li₂S–P₂S₅ glass-ceramic electrolytes were prepared by controlling the compositions and heat treatment temperatures of the glasses. The 70Li₂S·30P₂S₅ (mol%) glass-ceramic heated at 360 °C showed the highest conductivity of 3.2 × 10^− 3 S cm^− 1 at room temperature and the lowest activation energy of 12 kJ mol^− 1 for conduction in the binary system Li₂S–P₂S₅. The outstanding property was attributed to both the precipitation of the new crystal as a metastable phase and the increase in crystallinity of the phase. With increasing heat treatment temperatures, the metastable phase changed into thermodynamically stable phases such as the Li₄P₂S₆ crystal by heat treatment up to 550 °C, resulting in low conductivities of the glass-ceramics. It was, thus, found that the formation of superionic metastable phases by heating the Li₂S–P₂S₅ glasses is responsible for the marked enhancement on the conducting properties of the glass-ceramics.     

Free-volume defects investigation of GeS2-Ga2S3-CsI chalcogenide glasses by positron annihilation spectroscopy

The transformation behavior of free-volume defect in (80GeS₂-20Ga₂S₃)_100-x (CsI)_x (x = 0, 5, 10, 15 mol%) chalcogenide glasses was studied by employing positron annihilation spectroscopic technique, which could reveal valuable information for in-depth understanding of nano-structural defects in glassy matrix. The results indicate that the structural changes caused by CsI additives can be adequately described by positron trapping modes determined with two-state model. The initial addition of CsI (x = 5 mol%) led to a void contraction, whereas, the void agglomeration occurred with the increase of CsI and the free-volume defects of the glasses were obviously reduced. The atomic density ρ is inversely proportional to the number of these defects. Meanwhile, the UV cut-off edge shifts toward short-wavelength with increasing of CsI. This study provides the valuable information of defects evolution in GeS₂-Ga₂S₃-CsI glasses.     

Transport processes in heavy metal fluoride glasses

Na self-diffusion, Li self-diffusion, Na⁺–Li⁺ ion exchange, electrical conductivity, and mechanical relaxation have been studied below T_g on glasses of the system ZrF₄–BaF₂–LaF₃–AF (A=Na, Li), with A=10, 20, 30 mol%. Compared to the transport mechanism in alkali-containing silicate glasses, the mechanisms in these non-oxide glasses are anomalous. Thus the self-diffusion coefficient of Na decreases with increasing NaF content, whereas that of Li increases with increasing LiF content. Both the electrical conductivity and the Na⁺–Li⁺ ion exchange reach a minimum at ≈ 20 mol% LiF, and the mechanical relaxation shows one peak for the 20 and 30 mol% LiF-glasses and two peaks for the glass with 10 mol% LiF, evidencing both a contribution of F⁻ and Li⁺ ions to the transport. Moreover, the presence of the three partially interacting mobile species F⁻, Na⁺, Li⁺ obviously leads to an anionic–cationic mixed ion effect. Applying the Nernst–Einstein equation to the Li⁺ transport in LiF-containing glasses shows that its mechanism is dissimilar to that in oxide glasses. Calculated short jump distances possibly can be interpreted as an Li⁺ movement via energetically suitable sites near F⁻ ions. Likewise the Nernst–Planck model, successfully applied to the ionic transport in mixed alkali silicate glasses, obviously does also not hold for the present heavy metal fluoride glasses.     

Electric properties and structure of Agx(As0.33S0.335Se0.335)100−x bulk glasses

In this paper, results of investigation of the bulk glasses with composition of Ag_x(As_0.33S_0.335Se_0.335)_100−x (x=0–28 at%) are revealed. The amorphous structure of samples was confirmed by the X-ray diffraction analysis. The structure was deduced from the Raman spectra measured for all silver contents in As–S–Se matrix. From the point of their electrical properties, all glasses behave as ionic conductors. Their ac conductivity increases with increasing content of silver. As determined from the comparison of ac and dc conductivities, the contribution of electronic conductivity to the overall conductivity is very low and decreases from about 3% for the glass with 12 at% of Ag to about 1% for the glass with 22 at% of Ag.     

An efficient approach for the direct synthesis of lithium niobate powders

Lithium niobate powders from the raw powders of Li₂CO₃ and Nb₂O₅ are directly synthesized by a combustion method with urea as fuel. The synthesis parameters (e. g., the calcination temperature, calcination time, and urea-to-(Li₂CO₃ + Nb₂O₅) quantity ratio) are studied to reveal the optimized synthesis conditions for preparing high-quality lithium niobate powders. In our present work, it is found that a urea-to-(Li₂CO₃ + Nb₂O₅) ratio close to 3, calcination temperature at 550∼600 °C and reaction time around 2.5 h may lead to high-quality lithium niobate powders. The microstructure of synthesized powders is further studied; a possible mechanism of the involved reactions is also proposed.     

Erbium doping into silicate glasses to form luminescent optical layers for photonics applications

Here we summarise results of our research on the Er-containing thin surface layers in the silicate glasses and on the effect of the layers’ composition on their luminescence properties (emission at 1535 nm) in the wavelength region widely used in photonics. The optical layers were fabricated by Er³⁺ (melt)⇔Li⁺/Na⁺ (glass substrate) ion exchange in the specially designed Li₂O containing silicate glasses using various conditions (including annealing of the samples) to obtain a set of layers with diverse distribution of the Er³⁺ ions. Changes in the chemical composition of the prepared layers were suggested to avoid the concentration quenching effect and to improve their luminescence properties; special attention was paid to presence of hydrogen in the layers that may decrease the emission intensity. Rutherford Backscattering Spectroscopy and Elastic Recoil Detection were used to obtain detailed information on migration of erbium and hydrogen through the glass matrix, respectively. Photoluminescence spectra of the fabricated samples were measured (excitation at 980 nm) to examine the desired emission around 1535 nm.     

Broadband infrared luminescence in Yb-doped Bi2O3–GeO2 glasses

The Yb-doped Bi₂O₃–GeO₂ glasses were prepared by the conventional melt quenching technique. Near-infrared (NIR) broadband emission was found at about 1024 nm, and 1330 nm (under 785 nm excitation), and the measured fluorescent lifetime was about several hundred microseconds. The emission intensity of Yb-doped Bi₂O₃–GeO₂ glasses increased with increasing of Yb dopant in our experiments. The NIR emission should be related to Yb³⁺ and lower valence Bi ions.     

Effect of Ag addition on the third-order nonlinearity and physicochemical property of chalcohalide glass

In this work, the 70GeS₂–20In₂S₃–10CsI glass introduced with 0–10 mol% Ag₂S were prepared by the vacuumed melt-quenching technique. The physicochemical properties, such as glass transition temperature, density, refractive index, transmittance, hardness as well as third-order nonlinearity are investigated with the increasing Ag₂S contents. It was found that the refractive index (@632.8 nm), density, and hardness of glasses increase distinctly from 2.204 to 2.270, from 3.520 to 3.675 g cm⁻³ and from 180.9 to 227.9 kg mm⁻², respectively. Meanwhile, the nonlinear refractive index increases from 3.2 × 10⁻¹⁸ to 4.6 × 10⁻¹⁸ m²/W due to the increased refractive index. Finally, the Raman spectra are performed to structurally illustrate the role of Ag addition on the changes of the physicochemical properties. With the Ag₂S contents increasing, the vibration intensity of the [InS₄] and [InS₃I] tetrahedrons increases and the heavy Ag atoms result in the increased density and refractive index, as well as the nonlinear refractive index. The Ag-containing glass, which exhibited good thermal stability, excellent infrared transparency and ultrafast nonlinear optical properties, can be find applications for the IR window material or ultrafast infrared optics.     

Ionic conductivity in borate glasses with three types of mixed alkali cations

We have investigated the temperature- and frequency-dependent ionic conductivity in (Li_0.67 ? xNa_0.33 Rb_x)₂B₄O₇ (LNRBO) glasses with x = 0, 0.07, 0.2, 0.33, 0.47, and 0.6. The mixed alkali effect of the ternary mixed alkali system LNRBO is compared with that of the binary mixed alkali systems (Li_1 ? xNa_x)₂B₄O₇ (LNBO), (Li_1 ? xRb_x)₂B₄O₇ (LRBO) and the single alkali glass Rb₂B₄O₇ (RBO). From the results of the dc conductivity and dc activation energy, we observe that the LNRBO system exhibits the combined characteristic of binary mixed alkali systems LNBO and LRBO. It is found that the power-law exponent n for binary alkali glass is the same as that for ternary alkali glass but it is lower than that for single alkali glass. This indicates that the dimensionality of conducting pathway in the mixed alkali glasses of LNBO, LRBO and LNRBO is lower than that in the single alkali RBO. We discuss the concentration dependence of the dc conductivity and dc activation energy in the framework of the bond valence technique to reverse Monte Carlo produced structural model [Phys. Rev. Lett. 90, 155507 (2003)].     

Er–Pr doped tellurite glass nanocomposites for white light emitting diodes

In this paper, optical glass nanocomposites (nanoparticles sizes up to 100 nm) with composition TeO₂–WO₃–PbO–xEr₂O₃–yPr₆O₁₁ (x = 0.30 mol%, y = 0.70 mol%) embedded into polymer matrices was reported. The two types of polymers chosen for present study were: photopolymer oligoetheracryalte (OEA) and polymethylmethacrylate (PMMA), respectively. The incorporation of the titled nanoparticles into the polymer matrices is analyzed optically. The fluorescence spectra of the nanocomposites were compared with the fluorescence spectra of bulk glasses. Based on the comparison of Er^3 + and Pr^3 + ions' energy level schemes, possible energy transfer processes were identified. The prepared glasses are promising candidates for the white light emitting diodes applications.     

Preparation and properties of transparent SnO–P2O5 glasses

Colorless, transparent SnO–P₂O₅ (SP) glasses with 60–70 mol% SnO compositions were prepared by melting at 880–1000 °C in Ar atmosphere using commercial SnO and P₂O₅ powders as raw materials and vitreous carbon crucibles. SP glasses are characterized by glass transition temperature, onset of crystallization, thermal expansion coefficient and weight loss after immersion test. The viscosity of 67SnO–33P₂O₅ glass was measured by a penetration method in the range of 10^7.9–10^10.5 Pa s at 267–290 °C. The results of optical properties show that the transparent SP glasses have high refractive indexes over 1.75 and high transmission over 80% in the visible and IR region of 380 and 2700 nm.     

Synthesis and characterization of Ge and Sn(II) iodide-doped thioborate anhydrous proton conductors

Metal iodide-doped anhydrous proton conductors in the series xMI₂ + (1 − x)(HBS₂)₃, where M = Ge and Sn, have been prepared. These samples improve upon the anhydrous proton conductivity shown previously in the H₂S + B₂S₃ + GS_y series, where G = Si, Ge, and As, through a displacement reaction to incorporate HI into the materials. This is analogous to doping a silver halide salt into fast ion conducting chalcogenide glasses, such as AgI + Ag₂S + B₂S₃ + SiS₂, which results in a one to two orders of magnitude improvement in the ionic conductivity. The structural modification of the boroxol ring units in the thioboric acid is discussed based on the infrared and Raman spectroscopy. The DC conductivity, estimated from AC impedance spectra, of the metal iodide-doped (HBS₂)₃ samples is reported as a function of temperature and related back to the underlying structural chemistry of these materials. The static solid state proton NMR spectra were also used to identify the proton environment and proton dynamics. These materials represent an improvement upon previous anhydrous proton-conducting materials and represent an important step in finding intermediate temperature proton conductors.     

Structural,ferroelectric, optical properties of A-site-modified Bi0.5(Na0.78K0.22)0.5Ti0.97Zr0.03O3 lead-free piezoceramics

We reported the role of A-site modification on the structural, ferroelectric, optical and electrical field-induced strain properties of Bi_0.5(Na_0.78K_0.22)_0.5Ti_0.97Zr_0.03O₃ lead-free piezoceramics. The Li⁺ ions with concentration from 0 to 5 mol% were used to substitute at A-site. There was no phase transition when Li⁺ ions was added up to 5 mol%. The electric field-induced strain (S_max/E_max) values increased from 600 to 643 pm/V for 2 mol% Li⁺-added which results from distortion both rhombohedral and tetragonal phase structures. The band gap reduced from 2.88 to 2.68 eV and the saturation polarization decreased from 46.2 to 26.1 μC/cm² when Li⁺ ions concentration increased from 0 to 5 mol% respectively. We expect that this work could be helpful for further understanding the role of A-site dopants in comparison with B-site modification in lead-free Bi_0.5(Na,K)_0.5TiO₃-based ceramics.     

X-ray photoelectron spectroscopy of CeO2–Na2O–SiO2 glasses

A series of (CeO₂)_x–(Na₂O)_0.3–(SiO₂)_(0.7−x) glasses, where 0.025 ≤ x ≤ 0.075, have been synthesized and investigated by mean of X-ray photoelectron spectroscopy (XPS). The Ce 3d spin-orbit doublet was curve fitted in order to quantify the proportions of each cerium oxidation state in these glasses. It was found that Ce ions are predominantly in the Ce(III) state in glasses with compositions x ≤ 0.075, while mixed Ce valences were found in the glass with composition x = 0.10. The O 1s spectra have also been curve fitted with two components, one from bridging oxygen (BO) and the other from non-bridging oxygen atoms (NBO). The measured number of NBO, based on the fact that only oxygen atoms in the site Si–O–Na⁺ contribute to the NBO peak, was found to be constant at ∼35% for all samples, in good agreement with the value calculated from the glass composition and inductively coupled plasma (ICP) suggesting that Ce ions enter the network as a glass intermediate. The thermal measurements done on these glasses agree well with the XPS findings.     

X-ray excited luminescence and photoluminescence of Bi4(GeO4)3 glass-ceramics

Bi₄(GeO₄)₃ glass materials have been characterized by X-ray excited luminescence, photoluminescence and cathodo-luminescence measurements. The materials were obtained by crystallization at different temperatures and their spectroscopic parameters were compared before and after crystallization. Thermoluminescence curves recorded after electron irradiation of BGO glass behave similarly to BGO crystals, showing several peaks between 408 K (135 °C) and 610 K (337 °C). The differences between the Bi₄(GeO₄)₃ crystals and glass materials are believed to result from the random distribution of GeO₄ tetrahedra around Bi³⁺ ions which influences the photoluminescence and TL parameters. The CL images of glass-ceramic samples obtained by partial crystallization at 600 °C show luminescent crystalline structures, which are probably responsible for the increase in scintillation efficiency.     

Modeling and simulation of mid-IR amplifying characteristics of Tm3+-doped chalcogenide Photonic Crystal Fibers

This paper deals with the designing of a Tm³⁺-doped chalcogenide Photonic Crystal Fiber (PCF) amplifier operating in the mid-IR range. The chalcogenide glass of 72GeS₂–18Ga₂S₃–10CsI (in mol%) was fabricated with the high temperature melt-quenching method, which exhibited a strong emission peak around 3.8 μm under the excitation of a 800 nm laser. By employing the rate equations and propagation equations, the amplifying characteristics of the designed PCF amplifier were worked out. It is shown that the designed PCF amplifier exhibits a signal gain larger than 30 dB and a spectral width wider than 200 nm. The theoretical models and simulation results show that the PCF presented in this work can be used in developing high efficiency mid-IR light sources.     

Preparation of carbon nanoparticles from electrolysis of molten carbonates and use as anode materials in lithium-ion batteries

The electrochemical reduction of molten Li–Na–K carbonates at 450 °C provides “quasi-spherical” carbon nanoparticles with size comprised between 40 and 80 nm (deduced from AFM measurements). XRD analyses performed after washing and heat-treatment at various temperatures have revealed the presence of graphitised and amorphous phases. The d₀₀₂ values were close to the ideal one obtained for pure graphite. Raman spectroscopy has pointed out surface disordering which increases with increasing temperature of the heat-treatment. The presence of Na and Li on the surface of the carbon powder has been evidenced by SIMS. The maximum Na and Li contents were observed for carbon samples heat-treated at 400 °C. Their electrochemical performances vs. the insertion/deinsertion of lithium cations were studied in 1 M LiPF₆–EC : DEC : DMC (2 : 1 : 2). The first charge–discharge cycle is characterised by a high irreversible capacity as in the case of hard-disordered carbon materials. However, the potential profile in galvanostatic mode is intermediate between that usually observed for graphite and amorphous carbon: rather continuous charge–discharge curves sloping between 1.5 and 0.3 V vs. Li / Li⁺, and successive phase transformations between 0.3 and 0.02 V vs. Li / Li⁺. The best electrochemical performances were obtained with carbon powders heat-treated at 400 °C which exhibits a reversible capacity value of 1080 mAh g^− 1 (composition of Li_2.9C₆). This sample has also both the lowest surface disordering (deduced from Raman spectroscopy), and the highest Na and Li surface contents (deduced from SIMS).     

Influence of the selenium content on thermo-mechanical and optical properties of Ge–Ga–Sb–S chalcogenide glasses

A number of Ge₁₇Ga₄Sb₁₀S_69−xSe_x (x = 0, 15, 30, 45, 60, and 69) chalcogenide glasses have been synthesized by a melt-quenching method to investigate the effect of the Se content on thermo-mechanical and optical properties of these glasses. While it was found that the glass transition temperature (T_g) decreases from 261 to 174 °C with increasing Se contents, crystallization temperature (T_c) peak only be observed in glasses with Se content of x = 45. It was evident from the measurements of structural and physical properties that changes of the glass network bring an apparent impact on the glass properties. Also, the substitution of Se for S in Ge–Ga–Sb glasses can significantly improve the thermal stability against crystallization and broaden the infrared transmission region.